The invention concerns an interchangeable lens.
Interchangeable lenses of this type can be fitted to a system camera, such as a single-lens reflex camera or a metering viewfinder camera, with the aid of a locking device, usually in the form of a bayonet connection. The interchangeable lenses often have electrical loads, such as automatic focus and shutter adjusting mechanisms. For this reason, the bayonet connections have a plurality of electrical contacts, firstly to supply power to the electrical loads and secondly to transmit signals between the lens and camera housing. This multiplicity of electrical contacts, which are frequently arranged closely next to one another, are prone to defects. Undesired electrical connections between contacts which are not supposed to be connected to one another might occur, for example, when fitting a lens to the camera housing. EP 1 006 397 B1 discloses, in order to avoid these problems, the use of optocouplers for contactless optical signal transmission to separate the signal transmission from the power supply. Undesired short-circuits between signal connections and power supply connections of the lens and of the camera housing when the lens is fitted are reliably avoided in this way.
DE 34 38 322 A1 discloses a method for optical transmission of signal data between lens and camera in system cameras. In this case, defined radiation is produced which varies according to at least one mechanical manipulated variable in terms of at least one of its characteristics and is then converted to an electrical signal used to display the manipulated variable and/or to control camera functions. To this end, the camera housing contains means for producing defined radiation, and the lens has complicated optical means on the inside to receive and guide said radiation and also to return it to the camera housing. The lens additionally has means for varying at least one of the characteristics of said radiation according to at least one mechanical manipulated variable. Means for evaluating these variations in the radiation in view of the display of the manipulated variable and/or to control the camera functions are provided in the camera housing. The arrangement requires a large amount of space and many components, and the robustness of the bayonet mount on the lens side is affected by the light-passage openings. Retrofitting of existing lenses is impossible or possible only with considerable effort.
Another apparatus with optical recording of signal data can be found in DE 34 43 443 A1. The movement of lens mount and camera body relative to one another, which inevitably occurs when fitting the lens, is used to be able to record an optically readable scale in the form of a barcode on the camera lens. The barcode can be recorded only when the lens is being fitted. Malfunctions can occur while reading the scale, because the read apparatus always has to be ready to operate during the fitting process itself, but this instant is not known. Recording a barcode of an already fitted lens, for example after the camera is switched on, is not possible.